It looks like a few days ago a patch release of kitchen-inspec was pushed up to Rubygems that added test-kitchen ~> 1.6 to the dependencies. This causes a problem as the official install instructions are centered around chef gem install which does no cross-compat checks with the install test kitchen in ChefDK. I think a ChefDK release is in motion now to get 1.6 out to users, but we should all watch for this kind of thing in the future to try to reduce user frustration.